Sight in Flight: Astronaut Eyes in Microgravity

As space agencies and private organizations prepare for prolonged space missions, understanding how microgravity affects the human body is more important than ever. 

Approximately 60% of astronauts on extended missions experience significant changes to their eyesight—a condition known as Spaceflight-Associated Neuro-Ocular Syndrome (SANS). Protecting astronauts' vision is essential for the success and safety of future space exploration.

A Delicate Vision: How Microgravity Affects the Eyes

The eye, particularly the retina, is delicate and complex. Many astronauts who spend extended periods on the International Space Station (ISS) experience vision problems that can last for years. One major cause is believed to be the fluid shift toward the head, the cause of “moon face,” which increases pressure inside the skull. Elevated CO₂ levels on the ISS may also play a role (Marshall-Goebel, 2013; Corydon, 2023).

SANS: A Blurry Inconvenience 

Over a decade ago, NASA discovered that about 60% of astronauts showed signs of SANS. Surveys revealed that 29% of those on short missions and 60% on long ones reported farsightedness or nearsightedness. Some of these impairments last for years after returning to Earth (Mader, 2011).

Cellular Distortion: What’s Happening? 

An Italian research team elucidated the cellular effects of microgravity on retinal cells. Key findings included:

• Shifting Structures: The protein vimentin moved from the cell surface to the center, disrupting cell structure and function.
• Protein Traffic Jams: Issues with protein processing were observed, suggesting cellular dysfunction.
• Gene Chaos: Of 23,500 genes, more than 5,500 behaved abnormally compared to terrestrial controls (Cialdai, 2021).

Coenzyme Q10 (CoQ10) shows promise in mitigating these changes. This antioxidant positively impacted 153 genes and 22 cellular pathways, improving processes related to protein folding, cell survival, and aging. This makes CoQ10 a possible countermeasure for SANS (Cialdai, 2021).

Mice in Microgravity: Vision Under Pressure

In 2016, Mao et al. studied the retinas of mice after 35 days on the ISS, producing eye-opening findings: 

• Blood Vessel Breakdown: 64% more cell death in retinal blood vessels in microgravity. 
• Protein Disruption: Changes in proteins linked to inflammation, repair, and metabolism.
• Gravity’s Lifeline: Mice exposed to artificial gravity showed fewer harmful changes, suggesting it could protect against retinal damage (Mao, 2018).

Breaking Barriers: The Blood-Retina Barrier in Peril

A follow-up study revealed that microgravity damages the blood-retina barrier (BRB), which protects our eyes. Surprisingly, despite BRB damage, intraocular pressure decreased post-flight, defying typical expectations (Mao, 2019).

The Trifecta: Vision, Stress, and Gene Expression 

Overbey et al. investigated how microgravity alters retinal gene expression. They found:

• 600 Genes Off Track: Changes in genes related to photoreception and visual function.
• Oxidative Stress: Increased damage and reduced retinal layer thickness.
• Disease Links: Alterations in 12 genes associated with retinitis pigmentosa (Overbey, 2019).

Head Down, Eyes Up: Simulated Spaceflight on Earth

Laurie et al. used head-down tilt (HDT) to mimic microgravity. Their study found that HDT increased ocular pressure and optic nerve sheath size. Interestingly, elevated CO₂ levels did not worsen these changes (Laurie, 2017).

Genetic Clues: Why Some Eyes Fare Better

Zwart et al. discovered that genetic variations and B vitamin levels influenced the extent of optic disc swelling during simulated spaceflight. This finding could help develop personalized countermeasures (Zwart, 2019).

LBNP: Sucking Away the Pressure

Lower Body Negative Pressure (LBNP) uses suction on the lower body to redistribute fluids away from the head, mimicking ordinary gravity. This technique shows promise in reducing eye pressure and preventing SANS (Hall, 2024).

By simulating Earth’s gravity through rotating spacecraft or centrifuges, artificial gravity (AG) helps counteract fluid shifts. Research suggests AG supports cardiovascular health, balance, and eye function, making it a potential safeguard against SANS (Waisberg, 2024).

Conclusion: Keeping Our Eyes on the Stars

While LBNP, artificial gravity, and CoQ10 offer hope, there is always more to learn. 

This is why rapidly conducting experiments through simulated microgravity platforms, like Litegrav's, are indispensable. This allows researchers to study microgravity’s effects on vision and other bodily systems without the costs and constraints of spaceflight. By offering scalable, reproducible, and accessible simulated microgravity environments, Litegrav helps accelerate discoveries and optimize interventions, for clear sight in space and on Earth. 

References and Suggested Reading

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Chen, Z., Stanbouly, S., Nishiyama, N. C., Chen, X., Delp, M. D., Qiu, H., Mao, X. W., & Wang, C. "Spaceflight Decelerates the Epigenetic Clock Orchestrated with a Global Alteration in DNA Methylome and Transcriptome in the Mouse Retina." Precis Clin Med. 2021 May 17;4(2):93-108. doi: 10.1093/pcmedi/pbab012. PMID: 34179686; PMCID: PMC8220224.

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Cialdai, F., Bolognini, D., Vignali, L., Iannotti, N., Cacchione, S., Magi, A., Balsamo, M., Vukich, M., Neri, G., Donati, A., Monici, M., Capaccioli, S., & Lulli, M. "Effect of Space Flight on the Behavior of Human Retinal Pigment Epithelial ARPE-19 Cells and Evaluation of Coenzyme Q10 Treatment." Cell Mol Life Sci. 2021 

Dec;78(23):7795-7812. doi: 10.1007/s00018-021-03989-2. Epub 2021 Oct 29. PMID: 34714361; PMCID: PMC11073052.

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Corydon, T. J., Schulz, H., Richter, P., Strauch, S. M., Böhmer, M., Ricciardi, D. A., Wehland, M., Krüger, M., Erzinger, G. S., Lebert, M., Infanger, M., Wise, P. M., & Grimm, D. "Current Knowledge about the Impact of Microgravity on Gene Regulation." Cells. 2023 Mar 29;12(7):1043. doi: 10.3390/cells12071043. PMID: 37048115; PMCID: PMC10093652.

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Hall, E. A., Whittle, R. S., & Diaz-Artiles, A. "Ocular Perfusion Pressure is Not Reduced in Response to Lower Body Negative Pressure." npj Microgravity. 2024;10:67. doi: 10.1038/s41526-024-00404-5.

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Laurie, S. S., Vizzeri, G., Taibbi, G., Ferguson, C. R., Hu, X., Lee, S. M. C., Ploutz-Snyder, R., Smith, S. M., Zwart, S. R., & Stenger, M. B. "Effects of Short-Term Mild Hypercapnia during Head-Down Tilt on Intracranial Pressure and Ocular Structures in Healthy Human Subjects." Physiol Rep. 2017 Jun;5(11):e13302. doi: 10.14814/phy2.13302. PMID: 28611153; PMCID: PMC5471441.

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Mader, T. H., Gibson, C. R., Pass, A. F., Kramer, L. A., Lee, A. G., Fogarty, J., Tarver, W. J., Dervay, J. P., Hamilton, D. R., Sargsyan, A., Phillips, J. L., Tran, D., Lipsky, W., Choi, J., Stern, C., Kuyumjian, R., & Polk, J. D. "Optic Disc Edema, Globe Flattening, Choroidal Folds, and Hyperopic Shifts Observed in Astronauts after Long-Duration Space Flight." Ophthalmology. 2011 Oct;118(10):2058-69. doi: 10.1016/j.ophtha.2011.06.021. Epub 2011 Aug 17. PMID: 21849212.

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Mao, X. W., Nishiyama, N. C., Byrum, S. D., Stanbouly, S., Jones, T., Drew, A., Sridharan, V., Boerma, M., Tackett, A. J., Zawieja, D., 

Willey, J. S., Delp, M., & Pecaut, M. J. "Characterization of Mouse Ocular Response to a 35-Day Spaceflight Mission: Evidence of Blood-Retinal Barrier Disruption and Ocular Adaptations." Sci Rep. 2019 Jun 3;9(1):8215. doi: 10.1038/s41598-019-44696-0. PMID: 31160660; PMCID: PMC6547757.

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Mao, X. W., Sandberg, L. B., Gridley, D. S., Herrmann, E. C., Zhang, G., Raghavan, R., Zubarev, R. A., Zhang, B., Stodieck, L. S., Ferguson, V. L., Bateman, T. A., & Pecaut, M. J. "Proteomic Analysis of Mouse Brain Subjected to Spaceflight." Int J Mol Sci. 2018 Dec 20;20(1):7. doi: 10.3390/ijms20010007. PMID: 30577490; PMCID: PMC6337482.

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Marshall-Goebel, K., Barratt, M., & Gibson, C. "Ophthalmic Changes and Increased Intracranial Pressure Associated with Long Duration Spaceflight: An Emerging Understanding." Acta Astronautica. 2013;87:77–87. doi: 10.1016/j.actaastro.2013.01.014.

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Overbey, E. G., da Silveira, W. A., Stanbouly, S., Nishiyama, N. C., Roque-Torres, G. D., Pecaut, M. J., Zawieja, D. C., Wang, C., Willey, J. S., Delp, M. D., Hardiman, G., & Mao, X. W. "Spaceflight Influences Gene Expression, Photoreceptor Integrity, and Oxidative Stress-Related Damage in the Murine Retina." Sci Rep. 2019 Sep 16;9(1):13304. doi: 10.1038/s41598-019-49453-x. PMID: 31527661; PMCID: PMC6746706.

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Waisberg, E., Ong, J., Masalkhi, M., et al. "Artificial Gravity as a Potential Countermeasure for Spaceflight Associated Neuro-Ocular Syndrome." Eye. 2024;38:2847–2848. doi: 10.1038/s41433-024-03178-y.

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Zwart, S. R., Laurie, S. S., Chen, J. J., Macias, B. R., Lee, S. M. C., Stenger, M., Grantham, B., Carey, K., Young, M., & Smith, S. M. "Association of Genetics and B Vitamin Status with the Magnitude of Optic Disc Edema during 30-Day Strict Head-Down Tilt Bed Rest." JAMA Ophthalmol. 2019 Oct;137(10):1195-1200. doi: 10.1001/jamaophthalmol.2019.3124. PMID: 31415055; PMCID: PMC6696878.

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